Score another point for exogenesis, the idea that life on Earth has extraterrestrial origins. For the first time, NASA has identified amino acids in a sample of material from a comet, suggesting a comet may have brought proteins to Earth.

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In 2004, the NASA spacecraft Stardust captured particles shed by the Wild 2, an icy comet in our Solar System. Last year, the team examining the Wild 2 sample discovered it contained several amino acids as well as nitrogen-bearing amines. At the time, the team was unable to rule out contamination from Earth as a possible source of the amino acids. But after painstaking tests, they were able to determine that at least one of the amino acids, glycine, came from the comet itself.

Although discoveries like this by no means prove that life on Earth originated with a comet bringing amino acids into our atmosphere, the Stardust team is excited by the implications it has for eventually explaining the origins of life on Earth. And, combined with the recent discovery that some comets contain liquid water, it seems possible that comets strikes could bring the building blocks of life to a planet's surface. The next step is to obtain larger samples from comets, and samples from the comet's nucleus instead of its debris. Fortunately, the ESA'a Rosetta spacecraft is scheduled to land on the comet 67P/Churyumov-Gerasimenko in 2014, and will hopefully bring back just the sort of sample the Stardust team is longing for.